Kathy Nguyen was the fourth person this month to die from inhalation anthrax.

In New York, CNN's Jason Carroll filed this report.

CARROLL: Both the hospital and medical examiner's office confirmed that Kathy Nguyen, 61, died from complications of inhalation anthrax early this morning at 1:16 a.m. Nguyen worked at the Manhattan Eye, Ear and Throat Hospital, not too far from here. She worked in a stockroom located in the basement, in the same area as the mail room.

Just to give you some history of what happened here, she became sick on Thursday. She complained of having a headache and high fever. She went to work on Thursday, and work again on Friday. Over the weekend, her condition became much worse. Finally on Sunday, she checked herself into Lenox Hill Hospital. Doctors immediately put her on a respirator. Her condition at that point was critical.

This has been a baffling case for investigators because they simply have no idea how in the world Nguyen contracted this deadly disease. So what they are going to do is, they are going to retrace her steps. They have taken environmental samples from Manhattan, Eye, Ear and Throat Hospital. They have taken about 40 samples. Ten of those samples are back so far. Those samples have all turned up negative. They are also going to be taking environmental samples from her apartment in the Bronx.

They will also be interviewing her friends and her co-workers, trying to get some information, because unfortunately, Nguyen was so sick, she was unable to provide investigators with much in the way of helpful information. This is the first confirmed case of inhalation anthrax in New York City, and the first fatality.